Accurate modeling of nuclear-medicine collimators in Monte Carlo simulation of high-energy photons

Monte Carlo (MC) simulation of nuclear medicine imaging is more difficult f or procedures employing I-131 than for those using Tc-99m because of the hi gher probability of collimator penetration for the higher-energy I-131 gamm a. Additionally, an accurate model of the imaging camera must also simulate the scattering and penetration of photons emitted above the 364 keV photo peak (637 keV (6.5%) and 723 keV (1.7%)). Most MC codes used in nuclear med icine either employ severe approximations of the collimator interactions or have not been extended to higher energies. The MC program SKEPTIC, which h as previously been used to simulate slit aperture penetration of 511 keV ga mmas, has been modified to permit modeling of parallel hole collimators. We present here a comparison of measured and simulated energy spectra and poi nt spread functions for I-131. (C) 1999 Elsevier Science B.V. All rights re served.